Acrylonitrile-butadiene-styrene copolymer resin (hereinafter referred to as ‘ABS resin’) is a resin in which a copolymer of styrenic monomer and acrylonitrile monomer grafted to butadiene rubbery polymer (hereinafter referred to as ‘g-ABS’) is dispersed in a matrix of styrene-acrylonitrile copolymer resin (hereinafter referred to as ‘SAN’). ABS resin has a good balance of properties such as processability, impact resistance, chemical resistance, heat resistance and mechanical strength, and thus it has been widely used in the production of internal or external parts of electrical and electronic goods, parts of automobiles, general goods, and the like.
However, ABS resin can physically or chemically decompose during extrusion or injection molding and it easily darkens or turns yellow or forms a silver streak due to a thermal oxidation reaction, which makes it unusable in many products. Therefore, an antioxidant is generally added to ABS resin to reduce or prevent oxidation decomposition.
Antioxidants are typically classified as primary antioxidants such as hindered phenol compounds and secondary aromatic amines; and secondary antioxidants such as phosphites, thioesters and the like. Each antioxidant may provide good heat stability, and a combination of two or more antioxidants may provide even greater heat stability.
However, ABS resins are susceptible to surface appearance problems such as discoloration, gas silver and the like due to high shear stress and heat during mold processing of a thin film or a large-scale molded article, even when a combination of two or more of antioxidants is employed. Further, butadiene in ABS resin has poor weather resistance, and thus it is susceptible to photo-oxidation when ABS resin is exposed to exterior or outdoor environments over a long period of time. As a result, photo-oxidation can decompose or discolor ABS resin and decrease the light stability of ABS resin. Thus, there is a need to develop an ABS resin which has good stability to heat and light.
Polyester resins typically have a structure including short chains, and thus may not bend easily. Accordingly, polyester resins can have good rigidity, electrical properties, weather resistance and heat resistance, and the tensile strength of polyester resins may not be affected even after long term exposure to high temperatures. Further, polyester resins have good resistance to various oils such as diesel oil, and good dimensional stability and processability. Accordingly, polyester resins have been widely used in various industrial fields such as automobile parts, parts of electric and electronic goods and the like. Moreover, the surfaces of polyester resin articles have a good appearance, gloss and good plating properties, for example, good adhesiveness for aluminum vacuum plating or chrome plating, so that they are suitable for a headlamp bezel of a car.
However, ester bonds in the polyester chain are susceptible to hydrolysis so that the molecular weight of the polyester resins may decrease when they are exposed to high temperatures or high humidity over a long period of time. As a result, properties such as rigidity and impact resistance of polyester resins can be degraded.
Korean Patent No. 159,256 discloses a method of alloying polyester resin with ABS resin in order to solve the above problems. However, the polyester-ABS resin alloy has poor heat stability due to insufficient compatibility which may cause a gas release. Further, the alloy has poor impact strength due to the degradation of polyester resin.